1. Field of the Invention
The present invention relates to an apparatus to measure skin moisture content, which can reduce power consumption in a measurement standby mode, and more particularly, to an apparatus for measuring skin moisture content, which can connect a reference (R) electrode and a current (C) electrode in a measurement standby mode, and also can release the connection between the R electrode and the C electrode while the skin moisture content is measured from the skin of a user, and thereby can reduce the consumption of power spent before an electrode contacts with the skin of a user.
2. Description of the Related Art
As many people become interested in beauty, an interest in skin care has also increased. A desire for a healthy skin affects not only beauty-related businesses, but also affects the growth of medical-related businesses since people need to protect their skin from ultraviolet rays that have become stronger due to the destruction of the ozone layer, and various types of pollutions.
Skin is an organ of the integumentary system made up of multiple layers of epithelial tissues. Main functions of skin are protecting against pathogens, waterproofing, temperature regulation, insulation, and the like. One of the most critical elements to enable the proper performance of the functions of skin is moisture content in a stratum corneum. The moisture content in the stratum corneum is generally called a skin moisture content. When maintaining a particular moisture content in the stratum corneum, it is possible to perform basic functions of skin such as protecting against harmful substances like pathogens, and preventing excessive evaporation of skin moisture.
In view of skin care, the skin moisture content is also considered as an essential element. Accordingly, fundamental to skin care is skin moisture management.
According to a conventional art, an electrical measurement method, an optical measurement method, and a method using a magnetic resonance imaging (MRI) are included in a method of measuring skin moisture content. The electrical measurement method is widely used. More specifically, a method of measuring the skin moisture content by measuring susceptance, i.e. an alternating current (AC) component of admittance, of three electrodes, i.e. a reference (R) electrode, a current (C) electrode, and a measuring (M) electrode, using a sinusoidal wave of low frequency is generally used.
Among skin moisture content measuring apparatuses using the method of measuring susceptance, it is an issue that a portable skin moisture content measuring apparatus utilizes a maximum functionality within a limited power capacity. Specifically, what is important for any type of portable device is to reduce amounts of power consumption.
However, a conventional apparatus to measure skin moisture content consumes greater amounts of power in a measurement standby mode than when the skin moisture content is substantially measured, due to characteristics of an operational amplifier included in the apparatus for measuring skin moisture content. Specifically, when an electrode makes no contact with the skin of a user, an infinite load occurs in an output terminal of the operational amplifier due to a principle of the operational amplifier and thus, theoretically, an infinite amount of current may flow into a C electrode connecting with the output terminal. Accordingly, huge amounts of power may be consumed.
Specifically, when the electrode makes no contact with the skin of the user and thereby the operational amplifier is in an open loop state, an input impendence becomes almost infinite due to characteristics of the operational amplifier. Therefore, current supplied to the operational amplifier becomes zero, and an output impedance also becomes near zero. Accordingly, output current becomes infinite and thus a gain is also converged to infinity. Also, since the output terminal is in an open state, infinite loads appear to be loaded to the output terminal. Accordingly, to drive the infinite loads, the operational amplifier may try to draw a maximum current which can be inputted from a power source, and perform an output.
Specifically, when the electrode makes no contact with the skin, an input of a noninverting input terminal corresponding to +terminal becomes an input oscillation voltage Vin, and an input of an inverting input terminal corresponding to −terminal becomes a floating state, and thus any voltage Vx may be generated. Also, since the output terminal is in an open loop state without feedback, amplification may be infinitely performed in the output terminal. Therefore, although loads do not substantially occur, infinite loads and a virtual ground may be formed in the floating state. Accordingly, comparatively huge amounts of current may flow into a C electrode until a current control circuit operates in the operational amplifier.
However, when the electrode contacts with the skin of the user, the virtual ground is formed in the M electrode and thus the current flowing into the C electrode changes according to the strength of impedance of the stratum corneum right below the C electrode and the M electrode. In comparison to the measurement standby mode, a comparatively smaller amount of current may flow into the M electrode.
As described above, the conventional apparatus to measure skin moisture content consumes huge amounts of power in the measurement standby mode. Accordingly, there is a need for an apparatus to measure skin moisture content which can reduce power consumption in a measurement standby mode.